The aims of the core section of this program project are to further the development of the theoretical framework underlying the project for understanding normal and disordered cognition by exploring basic theoretical issues, and to foster the integration into the theoretical framework of constraints and research results arising from other approaches and methodologies. This part of the project will also proved shared resources that will support the four part projects. Two issues have emerged from our recent investigations as topics requiring focussed theoretical investigation: (1) The nature of the representations that are used in particular domains, and the constraints that shape and motivate their characteristics. (2) The nature and significance of the organization of the networks that subserve various aspects of cognition, and the reasons for their functional specialization. These issues will be addressed using simulation models based on the ideas that networks may be optimal or at least locally optimal solutions to an ensemble of constraints. Exploring how these constraints influence processing and learning in networks will be examined through computer modeling studies.